It's not like the talent trees, it's just things to unlock.

Some things can be unlocked or purchased. An example would be the species. You can either pay moneys or get one to 50 to unlock it and be able to use it for any class.

Some things can only be unlocked. This would be stuff like the class emotes, class buffs, and companion bonuses.

Some things can only be purchased. Ship upgrades (repair vendor, mailbox, neutral GTN, etc) fall under this.